Insulated gate bipolar transistor

ABSTRACT

A semiconductor device is disclosed. One embodiment provides a cell area and a junction termination area at a first side of a semiconductor zone of a first conductivity type. At least one first region of a second conductivity type is formed at a second side of the semiconductor zone. The at least one first region is opposed to the cell area region. At least one second region of the second conductivity type is formed at the second side of the semiconductor zone. The at least one second region is opposed to the cell area region and has a lateral dimension smaller than the at least first region.

BACKGROUND

In semiconductor devices such as Insulated Gate Bipolar Transistors(IGBTs) or Silicon-Controlled Rectifiers (SCRs) switching betweenoperation modes is accompanied by a change in the charge carrierdistribution within the device. This change in the charge carrierdistribution may be accompanied by such a change in the electric fielddistribution within the device that a current flow in short-circuit modebecomes destructive.

A need exists for a semiconductor device having improved short-circuitresistance.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1 illustrates a schematic cross-sectional view of a semiconductordevice portion in accordance with one embodiment.

FIG. 2A illustrates a schematic plan view on the sectional plane A-A′ ofFIG. 1 including a second region of circular shape in accordance withone embodiment.

FIG. 2B illustrates a schematic plan view on the sectional plane A-A′ ofFIG. 1 including a second region of elliptic shape in accordance withone embodiment.

FIG. 2C illustrates a schematic plan view on the sectional plane A-A′ ofFIG. 1 including a second region of circular ring-shape in accordancewith one embodiment.

FIG. 2D illustrates a schematic plan view on the sectional plane A-A′ ofFIG. 1 including a second region of octagonal ring-shape in accordancewith one embodiment.

FIG. 2E illustrates a schematic plan view on the sectional plane A-A′ ofFIG. 1 including a second region of rectangular shape with roundedcorners in accordance with one embodiment.

FIG. 3A is a diagram of equal dopant profiles of first and secondregions along cut lines B-B′ and C-C′ of FIG. 1 in accordance with oneembodiment.

FIG. 3B is a diagram of different dopant profiles of first and secondregions along cut lines B-B′ and C-C′ of FIG. 1 in accordance with oneembodiment.

FIG. 4 illustrates a schematic cross-sectional view of a semiconductordevice including second regions at a second side of a drift regionextending deeper into the drift region than a third region of equalconductivity type than the second regions.

FIG. 5 illustrates a schematic cross-sectional view of a semiconductordevice including a third region at a second side of a drift regionextending deeper into the drift region than second regions of equalconductivity type than the third region.

FIG. 6 illustrates a schematic cross-sectional view of a semiconductordevice including second regions at a second side of a drift regionextending deeper into the drift region than a fifth region of adifferent conductivity type than the second regions.

FIG. 7 illustrates a schematic cross-sectional view of a semiconductordevice including second regions at a second side of a drift regionextending deeper into the drift region than a third region of equalconductivity type than the second regions and a fourth region ofdifferent conductivity type than the second regions.

FIG. 8A illustrates a schematic cross-sectional view of a semiconductordevice including a plurality of first and second regions at a secondside of a drift region.

FIG. 8B illustrates a schematic plan view on a substrate portion of theIGBT of FIG. 8A.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

One embodiment provides a semiconductor device that includes a cell areaand a junction termination area at a first side of a semiconductor zoneof a first conductivity type. At least one first region of a secondconductivity type is formed at a second side of the semiconductor zone,the at least one first region being opposed to the cell area region.Furthermore, at least one second region of the second conductivity typeis formed at the second side of the semiconductor zone, wherein the atleast one second region is opposed to the cell area region and has alateral dimension smaller than the at least one first region.

FIG. 1 illustrates a schematic cross-sectional view of a portion of asemiconductor device 100 according to one embodiment. The semiconductordevice 100 includes a cell area 105 and a junction termination area 110at a first side 115 of a semiconductor zone 120 of a first conductivitytype. A first region 125 of a second conductivity type is formed at asecond side 130 of the semiconductor zone 120, the first region 125being opposed to the cell area region 105. A second region 135 of thesecond conductivity type is formed at the second side 130 of thesemiconductor zone 120, wherein the second region 135 is opposed to thecell area region 105 and has a lateral dimension d₂ smaller than thecorresponding lateral dimension d₁ of the first region 125.

A lateral direction 140 is a direction along a surface plane of thefirst side 115 or the second side 130. A vertical direction 145 is adirection perpendicular to a surface plane of the first side 115 or thesecond side 130.

The first conductivity type is different from the second conductivitytype. By way of example, the first conductivity type may be an n-typeand the second conductivity type may be a p-type. According to oneembodiment, the first conductivity type is the p-type and the secondconductivity type is the n-type.

The semiconductor device 100 may include further semiconductor regionsnot illustrated in FIG. 1. According to one embodiment, thesemiconductor device 100 may be an IGBT. According to one embodiment,the semiconductor device 100 may be an asymmetric SCR.

In the cell area 105 a plurality of transistor cells, e.g., Field EffectTransistor (FET) cells including gate structures, may be formed. In thejunction termination area 110 field plates and/or semiconductor regionssuch as field rings and/or variations of the lateral doping structuremay be formed to adjust a curvature of equipotential lines in a reverseblocking mode of the device 100.

The semiconductor zone 120 may be a drift zone and it may determine ablocking capability of the device 100, e.g., by its thickness and dopantprofile.

The first region 125 at the second side 130 may be an emitter region ata collector side of an IGBT. In a short-circuit mode of the device 100,the second region 135 may inject charge carriers into the drift zone 120compensating a current flow of charge carriers from within the driftzone 120 to a terminal at the second side 130. Thus, a shift of amaximum electric field within the drift zone 120 from the first side 115to the second side 130, and destructive currents such as currentfilaments in the area of the maximum electric field at the second side130 may be prevented. Hence, the short-circuit resistance of thesemiconductor device 100 may be improved by a suitable doping level ofthe first region 125.

Between the first region 125 and the junction termination area 110 aplurality of second regions 135 may be arranged. By way of example,these second regions 135 may be successively arranged along the lateraldirection 140 (not illustrated in FIG. 1). A lateral dimension of theplurality of second regions 135 successively arranged along the lateraldirection 140 may be equal (not illustrated in FIG. 1). According to oneembodiment, a lateral dimension of the plurality of second regions 135successively arranged along the lateral direction 140 may decrease fromthe first region 125 to the junction termination area 110 (notillustrated in FIG. 1). A lateral dimension of the second region 135along the lateral direction 140 may be in a range of 1 μm to 200 μm, inone embodiment between 2 μm to 100 μm such as between 5 μm to 50 μm. Atleast one of these second regions 135 may also be opposed to thejunction termination area 110 (not illustrated in FIG. 1).

FIG. 2A illustrates a schematic plan view on the sectional plane A-A′ ofFIG. 1 including the second region 135 of circular shape in accordancewith one embodiment.

Referring to FIG. 2B illustrating a schematic plan view on the sectionalplane A-A′ of FIG. 1, the second region 135 may also be of ellipticshape.

According to one embodiment illustrated in FIG. 2C, a schematic planview on the second region 135 along the sectional plane A-A′ of FIG. 1may be of circular ring-shape.

According to one embodiment illustrated in FIG. 2D, the second region135 may be of hexagonal ring-shape along the sectional plane A-A′ ofFIG. 1.

Referring to FIG. 2E illustrating a schematic plan view on the sectionalplane A-A′ of FIG. 1, the second region 135 may be of rectangular orsquare shape with rounded corners.

A shape of the second region 135 along the sectional plane A-A′ of FIG.1 may be of polyangular-shape, i.e., a hexagon, an octagon, a decagon.

FIG. 3A illustrates a diagram of equal dopant profiles 126, 136 of thefirst region 125 and the second region 135 along cut lines B-B′ and C-C′along a vertical direction 145 of FIG. 1 in accordance with oneembodiment. Equal dopant profiles 126, 136 for the first region 125 andthe second region 135 may be provided by a same photolithography andimplant of ions when forming these regions, for example.

According to one embodiment illustrated in FIG. 3B, a profile of thedopant concentration 126 of the first region 125 along the verticaldirection 145 into the semiconductor zone 120 differs from the profileof the dopant concentration 137 of the second region 135. The profile137 of the dopant concentration of the second region 135 includes amaximum dopant concentration less than the corresponding maximum dopantconcentration of the first region 125 and a depth of the second region137 into the semiconductor zone 120 is larger than the correspondingdepth of the first region 125 into the semiconductor zone 120.

According to one or more embodiments, the profile of the dopantconcentration of the first region 125 may differ from the correspondingprofile of the dopant concentration of the second region 135 by at leastone of maximum dopant concentration and extension depth into thesemiconductor zone 120 determined by implant dose and implant energy,for example. These profiles may also differ with regard to a dopantelement, i.e., material of dopant.

As a further example of a dopant concentration profile 138 of the secondregion 135 illustrated in FIG. 3B, the maximum dopant concentration andthe extension depth into the semiconductor zone 120 along the verticaldirection 145 may be less than the corresponding profile 126 of thefirst region 125. Different profiles of dopant concentration between thefirst region 125 and the second region 135 may be provided by usingdifferent photolithography for forming the first region 125 and thesecond region 135, i.e., any of different implant doses, implantenergies and dopant elements.

FIG. 4 illustrates a schematic cross-sectional view of a portion of anIGBT 200 in accordance with one embodiment. IGBT 200 includes atransistor cell area 205 and a junction termination area 210 includingsemiconductor termination regions 211 at a first side 215 of a driftzone 220 of a first conductivity type. In the transistor cell area 205an emitter side of IGBT 200 including source, body regions and gates maybe formed.

At a second side 230 of the drift zone 220, a collector side of IGBT 200is formed. At the second side 230, an emitter region 225 of a secondconductivity type different from the first conductivity type of thedrift zone 220 is formed. A distance d_(E) from a lateral edge of theemitter region 225 to a lateral edge of the transistor cell area 205along a lateral direction 240 may be in a range of several 10% toseveral 100% of a diffusion length of minority charge carriers withinthe drift zone 220. Second regions 235 of the second conductivity typeare formed at the second side 230 between the emitter region 225 and thejunction termination area 210. The second regions 235 are consecutivelyarranged along the lateral direction 240 from the emitter region 225 tothe junction termination area 210. The dopant profile of the secondregions 235 along a vertical direction 245 may correspond to the dopantprofile of the emitter region 225, i.e., these regions may be formed bya same implant in a same lithography step. Each of the second regions235 may have a same lateral dimension d₁ along the lateral direction240. According to one embodiment, a lateral dimension of the pluralityof second regions 235 successively arranged along the lateral direction240 may decrease from the emitter region 225 to the junction terminationarea 210 (not illustrated in FIG. 4). A third region 250 of the secondconductivity type is formed at the second side 230 of the drift zone 220opposed to both the transistor cell area 205 and the junctiontermination area 210. A maximum dopant concentration of the third region250 may be smaller than the maximum dopant concentration of each of thesecond regions 235 and of the emitter region 225. A vertical extensionof the third region 250 into the drift zone 220 along the verticaldirection 245 is smaller than the corresponding vertical extension ofeach of the second regions 235 into the drift zone 220.

The second regions 235 may be configured to inject a minor amount ofcharge carriers into the drift zone 220 during a conductive mode of IGBT200, but may inject enough charge carriers in a short-circuit mode toavoid a shift of a maximum electric field along the vertical direction245 from the first side 215 to the second side 230 of the drift zone220.

FIG. 5 illustrates a schematic cross-sectional view of a portion of anIGBT 300 according to one embodiment. Similar to IGBT 200 illustrated inFIG. 4, IGBT 300 includes a transistor cell area 305 and a junctiontermination area 310 including semiconductor termination regions 311 ata first side 315 of a drift zone 320 of a first conductivity type. At asecond side 330 of the drift zone 320 constituting a collector side ofIGBT 300, an emitter region 325 of a second conductivity type and secondregions 335 of a second conductivity type are formed. A third region 350of the second conductivity type having a smaller maximum dopantconcentration than each of the second regions 335 is formed at thesecond side 330. Different from the third region 250 of IGBT 200illustrated in FIG. 4, the third region 350 has a vertical extensionalong the vertical direction 345 into the drift zone 320 that is largerthan the corresponding vertical extension of each of the second regions335 into the drift zone 320.

With regard to the schematic cross-sectional view of a portion of anIGBT 400 illustrated in FIG. 6, a transistor cell area 405, a junctiontermination area 410 including semiconductor termination regions 411, anemitter region 425 at a collector side of a drift zone 420 and aplurality of second regions 435 are formed similar to the correspondingelements 205, 210, 211, 225 and 235 of the embodiment illustrated inFIG. 4. In addition, a fifth region of the first conductivity type,i.e., a conductivity type different from the conductivity type of theemitter region 425, is formed at the second side 430 of IGBT 400, thefifth region being at least partly opposed to the junction terminationarea 410 at the first side 415 of the drift zone 425. A verticalextension of the fifth region 460 along a vertical direction 445 intothe drift zone 420 is smaller than the corresponding extension ofemitter region 425 into the drift zone 420. A maximum dopantconcentration of each of the second regions 435 may be larger than themaximum dopant concentration of the fifth region. IGBT 400 may be areverse-conducting IGBT.

With regard to the schematic cross-sectional view of a portion of anIGBT 500 illustrated in FIG. 7, a transistor cell area 505, a junctiontermination area 510 including semiconductor termination regions 511, anemitter region 525 at a collector side of a drift zone 520 and aplurality of second regions 535 and a third region 550 are formedsimilar to the corresponding elements 205, 210, 211, 225, 235 and 250 ofthe embodiment illustrated in FIG. 4. In addition, a fourth region 570of the first conductivity type, i.e., a conductivity type different fromthe conductivity type of the emitter region 525, is formed at a secondside 530, i.e., a collector side, of IGBT 500. The fourth region may bea field stop zone and it may extend deeper into the drift zone 520 thanthe emitter region 525. The field stop zone may be formed by implant ofH⁺ ions with a subsequent annealing such as annealing at temperatureswithin a range of 350° C. to 420° C., or by diffusion of P or Se, forexample.

FIG. 8A illustrates a schematic cross-sectional view of a portion of anIGBT 600 according to one embodiment. A transistor cell area 605 isformed at a first side 615 of a drift zone 620 of a first conductivitytype. At a second side 630 of the drift zone 620 a plurality of emitterregions 625 of a second conductivity type different from the firstconductivity type are formed. In addition to the emitter regions 625, aplurality of second regions 635 of the second conductivity type areformed at the second side 630 of the drift zone 620. A lateral dimensiond₂ of each of each of the second regions 635 along the lateral direction640 is smaller than a corresponding lateral dimension d₁ of each of theemitter regions 625. In addition to the emitter regions 625 and thesecond regions 635, a third region 650 of the second conductivity typeis formed at the second side 630 of the drift zone 620. A maximum dopantconcentration within the third region 650 is smaller than a maximumdopant concentration within each of the emitter regions 625. Furthersecond regions 635 may be arranged in a transition region between thetransistor cell area 605 and a junction termination area (notillustrated in FIG. 8A).

FIG. 8B illustrates a schematic plan view on IGBT 600 of FIG. 8A. Thecross-sectional view illustrated in FIG. 8A is taken along intersectionline A-A′. The plurality of emitter regions 625 are arranged in fourareas 670, 671, 672 and 673. In a space between these areas 670, 671,672 and 673, the plurality of second regions 635 are arranged. A varietyof different arrangements of emitter regions 625 and second regions 635may be provided and the specific arrangement illustrated in FIG. 8B ismerely an example of positioning the emitter regions 625 and the secondregions 635 having different lateral dimensions.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. An insulated gate bipolar transistor, comprising:a transistor cell area including source, body regions, and gates and ajunction termination area at a first side of a semiconductor zone of afirst conductivity type; an emitter region of a second conductivity typeat a second side of the semiconductor zone, the emitter region beingopposed to the cell area region; at least one second region of thesecond conductivity type at the second side of the semiconductor zone,wherein the at least one second region is opposed to and covered by thecell area region and each of the at least one second region is disposedat a lateral distance from the emitter region and has a lateraldimension smaller than the emitter region, and wherein the at least onesecond region is configured to inject charge carriers into thesemiconductor zone via a terminal at the second side; and a third regionof the second conductivity type at the second side of the semiconductorzone, the third region being arranged in an area including at least partof both the emitter region and the at least one second region, andwherein a maximum dopant concentration of the third region is smallerthan the maximum dopant concentration of the emitter region, wherein theat least one second region is arranged between the emitter region andthe junction termination area; and wherein each of the emitter region,the at least one second region and the third region extend from a commonsurface at the second side into the semiconductor zone.
 2. The insulatedgate bipolar transistor of claim 1, wherein a material of dopant and adopant profile of the at least one second region corresponds to thematerial of dopant and the dopant profile of the emitter region,respectively.
 3. The insulated gate bipolar transistor of claim 1,wherein the at least one second region includes a plurality of secondregions successively arranged in a direction from the emitter region tothe junction termination area.
 4. The insulated gate bipolar transistorof claim 1, wherein a lateral dimension of the at least one secondregion along a direction from the emitter region to the junctiontermination area is in a range of 2 μm to 100 μm.
 5. The insulated gatebipolar transistor of claim 1, further comprising: a fourth region ofthe first conductivity type at the second side of the semiconductorzone, a vertical distance of the fourth region to the first side beingsmaller than the corresponding vertical distance of the emitter regionto the first side.
 6. An insulated gate bipolar transistor, comprising:a transistor cell area including source, body regions, and gates and ajunction termination area at a first side of a semiconductor zone of afirst conductivity type; an emitter region of a second conductivity typeat a second side of the semiconductor zone, the emitter region beingopposed to the cell area region; at least one second region of thesecond conductivity type at the second side of the semiconductor zone,wherein the at least one second region is opposed to and covered by thecell area region and each of the at least one second region is disposedat a lateral distance from the emitter region and has a lateraldimension smaller than the emitter region, and wherein the at least onesecond region is configured to inject charge carriers into thesemiconductor zone via a terminal at the second side; and a fifth regionof the first conductivity type at the second side of the semiconductorzone, the fifth region being at least partly opposed to the junctiontermination area, wherein the at least one second region is arrangedbetween the emitter region and the junction termination area; andwherein a vertical extension of the fifth region along a verticaldirection into the semiconductor zone is smaller than the correspondingextension of the emitter region into the semiconductor zone.
 7. Theinsulated gate bipolar transistor of claim 6, wherein the at least onesecond region includes a plurality of second regions successivelyarranged in a direction from the emitter region to the junctiontermination area.